Applications requiring a controller for controlling a process variable are various. For example, a closed-loop controller may be used to control the output voltage of a power supply used to power a power amplifier. The current drawn by the power amplifier relates to its present input/output power which changes dynamically and therefore has a wideband spectrum. The alternating current, in turn, modulates the output voltage of the power supply since its output impedance is not indefinitely low. In order to avoid an undesirable drop of output voltages, controllers, e.g. closed-loop controllers, may be used to dynamically control the output voltage provided by the power supply. In order to avoid introduction of additional noise into the output signal provided by a power amplifier, e.g. a mobile communication Radio Frequency (RF) amplifier, power supplies should have low impedance in the bands where low noise is required or noise components introduced by the power supplies should be cancelled within those bands.